A shearer attachment closes its jaw by extending an actuating rod of an actuating cylinder (hydraulic cylinder), and opens the jaw by retracting the actuating rod. Because the operation of extending the actuating rod generates a strong force, the extending operation is suitable for crushing work in which the jaw is closed to nip an object to be crushed. Such a shearer attachment has an acceleration circuit for increasing the moving speed of the actuating rod, and reduces the working hours required in crushing by accelerating the operation of extending the actuating rod while no load is applied thereto (with no object to be crushed nipped in the jaw). The operation of retracting the actuating rod is used to open the jaw, which does not require a strong force.
Patent Literature 1 discloses an acceleration circuit for accelerating the operations of extending and retracting the actuating rod. The acceleration circuit disclosed in the Patent Literature 1 is provided with an inversion cylinder, separately from the actuating cylinder for opening and closing the jaw, for example (claim 1, Patent Literature 1), and the inversion cylinder and a bottom-side upstream switching valve are used to switch between a mode for prioritizing the flowrate and that for prioritizing thrust. When the actuating rod is to be extended, the acceleration circuit disclosed in Patent Literature 1 increases the flowrate of the oil to be supplied into the bottom-side chamber of the actuating cylinder. When the actuating rod is to be retracted, the acceleration circuit reduces the flowrate of the oil discharged from the bottom-side chamber of the actuating cylinder. By reducing a loss in the pressure, and increasing the flowrate of the oil sent out from the pump in the manner described above, the speed at which the actuating rod is extended and retracted is increased ([0010], Patent Literature 1).